Specific Aim 1A: To quantify the effect of ritonavir on VLDL production and clearance using stable isotope turnover and other clearance methods.

Specific Aim 1B: To determine the composition of the triglyceride rich particles.

Protocol 1: The effects of ritonavir-based regimens on VLDL production, VLDL clearance and triglyceride-rich lipoprotein composition in healthy normal volunteers. HIV-seronegative volunteers will be studied before and at the end of four weeks of taking ritonavir, lopinavir/ritonavir or atazanavir/ritonavir.

Hypothesis 2: NNRTI drugs do not increase HDL by increasing apo AI production, but rather by decreasing apo AI clearance, prolonging time in circulation.

Specific Aim 2A: To determine the composition of HDL before and after NNRTI and assess its function.

Specific Aim 2B: To quantify the effect of NNRTI on apo AI production and clearance using stable isotopes.

Specific Aim 2C: To determine if the NNRTI induced increase in HDL is accompanied by improvement in flow mediated vasodilation and circulating markers of endothelial function Protocol 2A: The effects of efavirenz on HDL composition, HDL function, apo AI production, apo AI clearance, flow mediated vasodilation and circulating markers of endothelial dysfunction in healthy normal volunteers. HIV-seronegative volunteers will be studied before and at the end of six weeks of taking efavirenz.

Protocol 2B: The effects of starting an efavirenz-based regimen on HDL composition, HDL function, apo AI production, apo AI clearance, flow mediated vasodilation and circulating markers of endothelial dysfunction in patients with HIV infection. HIV-infected patients whose care providers have prescribed an efavirenz-based regimen will be studied before and after six weeks of starting efavirenz.

Protocol 3: The effects of ritonavir-based regimens on insulin secretion in healthy normal volunteers. HIV-seronegative volunteers will be studied before and at the end of four weeks of taking ritonavir, lopinavir/ritonavir or atazanavir/ritonavir.

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Please refer to this study by its ClinicalTrials.gov identifier: NCT00525239